Storage tank



W. R. HNOT April 7, 1970 STORAGE TANK 2 Sheets-Sheet 2 Filed Sept. 30, 1968 INVENTO #441? Riva;- BY F Z Z ATTORNEY United States Patent O 3,504,496 STORAGE TANK Walter R. Hnot, Mountainside, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware Filed Sept. 30, 1968, Ser. No. 763,526 Int. Cl. B65g /00; E21f 17/16 US. Cl. 61--.5 Claims ABSTRACT OF THE DISCLOSURE A low evaporative loss open pit storage reservoir for liquid hydrocarbons includes a relatively thin barrier wall means to define an internal enclosure within the open pit. The barrier wall means is supported from the bottom of the open pit with the lower edge of the wall means in raised spaced relationship to the pit bottom to permit free passage of a surrounding body of ballast water to the bottom of the enclosure so that as hydrocarbon liquid is pumped into and out of the enclosure the hydrostatic balance between the surrounding water and the hydrocarbon is always maintained. Excessive water buildup due to rain accumulation within the surrounding body of ballast water is overflowed to a drainage system.

BACKGROUND OF THE INVENTION Large volumes of residual fuel oil have been economically stored in earthen reservoirs or pits. Because of the expense and difficulty in providing a floating roof having a perimeter capable of effectively sealing with the pit edges, such pits have usually been left open at the top. The product chosen for storage therefore could not be very volatile and had to be limited to the heavier residual fuels. The evaporative loss in these open pits is in the neighborhood of 1% and this loss being in the more expensive lighter ends such as, kerosene, etc., has to be subsequently blended in to bring the oil back to specification before shipment.

In addition to the product loss by evaporation, there are problems of possible odor, danger to wildlife, and surface contamination. It is therefore desirable to provide an economical floating roof or cover on open pit storage reservoirs so that in addition to correcting these problems, it would also be possible to store some of the other refinery product or crudes that are more volatile.

While the obvious way of storing volatile hydrocarbon liquids is to provide a conventional steel tank, the largest tanks to date are approximately 300 ft. in diameter and structurally require bottom course plates of approximately 1 /2 inch thickness of high strength steel. As tanks increase in diameter, it is necessary to go to thicker steel plates due to increased hoop stresses. Accordingly, to date 300 ft. diameter is approximately the maximum feasible diameter for conventional closed or floating roof steel storage tanks.

DESCRIPTION OF THE INVENTION In one form, the present invention is a hybrid storage tank which in effect is a cross between an open pit storage tank with sloping sides and a cylindrical metal storage tank with vertical sides. The invention makes possible a storage tank having the diameter of 1,000 ft. and a height of 70 ft. or more with walls of normal strength steel less than 1 /2 inches thick. The tank in accordance with the invention does not use a steel bottom and unlike irregular or sloping side storage pits may employ a simple floating roof design having constant peripheral diameter in order to make a continuous and good evaporative loss seal with the edge of the cylindrical walls of the tank independent of hydrocarbon levels therein.

While the prior Cornell et al. Patent No. 2,798,633 discloses hydrostatic balancing techniques for reducing the steel wall thickness of storage tanks from that which would ordinarily be required, schemes such as disclosed in this patent are not practical from a cost and efficiency standpoint. In accordance with the prior art, the vertical steel barrier wall was suspended by a plurality of floats and as the amount of stored oil changed, the entire suspended Wall structure moved vertically to assume a new vertical height relative to the reservoir walls. Obviously, the effective storage capacity of the prior art structures is limited by the depth to which the floating wall can sink in the reservoir because hydrostatic balance would disappear when the lower edge of the wall contacted the reservoir bottom. In applicants invention unlike the complex support scheme of the foregoing US. patent, the vertical walls are permanently fixed by structural means in a vertical relationship to the bottom of an earth storage pit. A passageway is provided under or through the lower edge of the vertical wall to permit free access of the water ballast liquid from the exterior to the interior of the enclosure defined by the steel walls. In this way, because of applicants permanently fixed vertical walls, the elaborate floatation arrangements of the prior art are avoided and maximum oil storage capacity is obtained for the amount of steel employed independent of the overall depth of the reservoir.

Accordingly, it is the principal object of the invention to provide an improved low cost hydrocarbon liquid storage reservoir having a minimum evaporative loss and a substantially uniform diameter floating roof cover.

Another object of the invention is to provide an economical floating roof cover for an open storage pit.

Another object of the invention is to provide an economical hydrocarbon liquid storage tank design with minimum evaporative loss, minimum thickness of ordinary carbon steel, and maximum capacity for the amount of carbon steel employed.

Another object is to provide an improved low cost floating roof oil storage tank of exceedingly large diameter in excess of economical conventional storage steel tank designs.

These and other objects and advantages of the invention will become apparent and the invention will be fully understood from the following description and drawings in which:

FIG. 1 is a side elevation view partially in section showing one form of the invention;

FIG.2 is a view similar to FIG. 1 showing the reservoir of FIG. 1 with a minimum amount of hydrocarbon liquid therein;

FIG. 3 is a perspective view of a tank similar to FIG. 1 showing additional side braces;

FIG. 4 is a view similar to FIG. 1 showing yet another embodiment of the invention as it would be employed in a quarry pit having substantially vertical but irregular sides; and

FIG. 5 is a view similar to FIG. 1 showing yet another embodiment of the invention wherein maximum storage capacity is obtained with the use of a minimum of ballast water.

Referring to FIGS. 1 and 2 in particular, one form of the invention is shown wherein an open pit reservoir generally designated 10 includes a pair of opposed sloping side wall embankments 12. Within the open pit there is a vertical barrier wall 16 which may be cylindrical in shape which is held in its vertical position by a plurality of pilings 14 which surround its exterior periphery and are driven downwardly into the soil structure. The vertical barrier wall 16 will be understood to be fixedly fastened to the pilings 14 by conventional fastening means (not shown). The top edge of the wall 16 includes a stiffening wind girder 17 which may be further rigidified by a plurality of radially extruding cables 19 fastened to the embankment 12 (see FIG. 3). The open pit reservoir includes a body of ballasting water 22 which extends about the periphery of the embankment 12 and also underneath the lower edge of the barrier wall 16 to underly a body of stored hydrocarbon liquid designated 24 within the barrier wall. Due to the difference in specific gravity between water and hydrocarbon liquids a hydrostatic balance therebetween is obtained wherein the upper level of the oil 24 is slightly above the upper level of the water 22. In this way the structural stress that the vertical wall 16 experiences is limited to the difference between the hydrostatic water pressure on one side of the vertical wall and the oil-water static pressure on the other side of the vertical Wall. This differential pressure is zero at the bottom of the vertical wall 16 and a maximum at the top water line as shown. Accordingly, due to the substantially complete pressure balancing across wall 16 of the structural strength of the wall and its thickness may be relatively small and will be substantially less than that which would ordinarily be required if the wall had to contain the entire load of the tank contents as in an above ground conventional steel storage tank.

The upper surface of the oil 24 supports a conventional floating roof 18 which includes annular bouyancy chambers 21 and a peripheral seal 20. The roof seal arrangement is therefore effective to float up and down with the oil level substantially engaging the vertical walls of the barrier 16 to eliminate and reduce evaporative loss of the hydrocarbon 24 to the atmosphere, The pit 18 is provided with a suitable oil pumping conduit means 62 connected by a transfer line 63 to a pump 64. Therefore as the pump 64 removes oil from the storage reservoir the floating roof will descent as the level of the oil decreases while maintaining a uniform and positive suction inlet point from the reservoir. The roof 18 includes a clearance dome 23 to permit maximum settling of the roof and therefore maximum removal of oil.

In FIG. 2 it may be seen that as the hydrocarbon 24 is removed from the reservoir the level of the water has lowered in the moat about the outside of the barrier 16 as more and more water has entered and passed below the lower edge of wall 16 to hydrostatically balance the smaller quantity of oil 24. In other words, as oil is removed the interface 26 between the water and oil gradually rises. The embankment 12 is provided with an overflow conduit 28 which may be connected to a conventional drainage sewer. The operation of the overflow is such that should there be an excessive amount of rain or ground Water accumulation in the moat about the barrier 16, it will drain off through the conduit 28 prior to overflowing the oil above the top edge of the wall 16. Accordingly, the weir defined by the vertical positioning of the inlet edge of the conduit 28 is at all times below the upper edge of the barrier wall 16.

Referring to FIG. 3 additional supports for the upper edge of the barrier wall 16 are shown in the form of cables 19. These cables in conjunction with the girders 17 assure constant and uniform shell curvature which is desirable for optimum performance of the seal 20.

In FIG. 4 a still further embodiment of the invention is shown wherein the invention is incorporated into a subterranean type quarry structure or pit. The quarry pit includes side Walls 44 to which are attached a plurality of truss supports 42 which secure the vertical barrier wall 40 in the relationship shown. As in the previous embodi ments an overflow conduit 46 for ballast water is provided having an inlet weir level sufiiciently low to prevent overflow of oil over the top of the wall 40 upon increase in quantity of balancing water due to rain or ground water seepage, A conventional floating roof 48 similar to that of FIG. 1 is employed.

Referring to FIG. 5, another embodiment is shown wherein a minimum of ballast water is employed. Specifically, the vertical metallic barrier wall 50 is supported by a plurality of pilings 52 with its lower edge in contact with the embankment 12. Extending through the barrier wall at the lower portion thereof is an inclined water transfer conduit 54 having its lower end in communication with an annular trench 60 extending about the inside periphery of the vertical barrier 50. A conventional floating roof S6 is employed. In this arrangement a maximum quantity of oil may be stored with a minimum amount of area of barrier 50 due to the fact that a minimum of ballast water is provided. Excess ballast water, as in the previous embodiments, is discharged about the periphery of the storage pit over a weir 58 again disposed lower than the top edge of barrier 50.

Another feature of the invention is that it may be located upon poor load bearing soils, such as, for instance, a marsh, where conventional tankage would normally be limited in height or require expensive foundation or piling supports. This is because the load of the stored oil and floating roof will be carried by displaced ground Water.

While several specific embodiments of the invention have been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. A low evaporative loss open pit storage reservoir for hydrocarbons comprising a sloping embankment defining the periphery of said reservoir, barrier wall means defining an enclosure within said reservoir, support means for said wall means, said support means maintaining said wall means in a substantially vertical position adjacent said sloping embankment with the lower edge of said wall means in raised and fixed spaced relationship to the bottom of said reservoir to establish therewith a predetermined gap and permit free passage of fluid thereunder, a body of water between said embankment and the wall means, a body of liquid hydrocar- =bon within the enclosure defined by said barrier wall means, said body of water extending under said wall means and beneath said hydrocarbon, and a floating roof supported by the body of said liquid hydrocarbon within the enclosure for reducing evaporative loss thereof.

2. The combination of claim 1, wherein said enclosure is circular and said floating roof includes flexible seal means in engagement with the interior of said wall means.

3. The combination of claim 2, wherein said support means includes a plurality of piles about the outside periphery of said wall means, said piles extending downwardly into the bottom of said reservoir and a plurality of radially bracing means extending outwardly from said wall means to said embankment.

4. The combination of claim 3, wherein the bottom and sloping embankment of said reservoir includes a substantially liquid impervious lining for preventing loss of water to the soil.

5. The combination of claim 3, wherein the bottom and sloping embankment of said reservoir comprises a cement stabilized soil.

6. The combination of claim 1 including water overflow means to limit the upper level of said water around said wall means and discharge excess water from said reservoir.

7. The combination of claim 6 including conduit means for transferring hydrocarbon liquid to the interior of said barrier wall means.

8. A low evaporative loss open pit storage reservoir for hydrocarbons comprising, a sloping embankment defining the side walls and periphery of said reservoir, barrier wall means defining an enclosure, support means for said wall means, said support means maintaining said wall means in a substantially vertical position adjacent said sloping embankment with the lower edge of said wall means in sealing relationship with a lower portion of the sloping wall means of said reservoir, an annular trench interior and adjacent the bottom of said wall means, said trench extending below the plane of the bottom of said reservoir, a body of water between said embankment and the wall means, and filling said trench, conduit means placing said trench in fluid communication with the area between said embankment and said wall means, a body of liquid hydrocarbon within the enclosure of said wall means, and a floating roof supported by the body of said liquid hydrocarbon within the enclosure for reducing evaporative loss thereof.

9. The combination of claim 8, wherein the bottom and sloping embankment of said reservoir comprises a cement stabilized soil.

10. The combination of claim 8 including water overflow means to limit the upper level of said water around said wall means and discharge excess water from said reservoir.

References Cited UNITED STATES PATENTS 1,561,260 11/1925 Mallery 61.5 2,211,958 8/1940 Mahatfey 61.5 3,052,380 9/1962 Prins 61.5 3,096,902 7/1963 Schroeder 61-.5 3,330,118 7/1967 Biais 61.5

FOREIGN PATENTS 1,133,581 11/1968 Great Britain.

PETER M. CAUN, Primary Examiner 

